Receiving antenna distribution systems operate at low power levels and are built to fit
a standard 19-inch rack. Each piece of distribution equipment is fitted with termination
or patch fittings designed for ease of connecting and disconnecting. A basic patch panel
is shown in figure 3-11. Even a fundamental distribution system has several antenna
transmission lines and several receivers. Normally a patch panel consists of two basic
patch panels. One panel is used to terminate the antenna transmission lines and the other
the lines leading to the receivers. Any antenna can be patched to any receiver through the
use of patch cords.

Figure 3-11. - Basic rf receive patch panel.

Many distribution systems are more complex. A complex distribution system to cover most
situations is illustrated in figure 3-12. In this system you can patch four antennas to
four receivers, or you can patch one antenna to more than one receiver via the
multicouplers (multicouplers are covered later in this chapter). You can also patch rf and
audio from one compartment to another. A frequency standard is connected (through a
distribution amplifier not shown) to the receivers.

Figure 3-12. - Complex distribution system.

Transmitting antenna distribution systems perform the same functions as receiving
systems. However, because of the higher power levels, design and fabrication problems are
more difficult. The ideal design would be to have all the transmission lines designed for
the highest power level. But because high-power patch cords are expensive, large, and
difficult to handle, this approach is seldom followed.

In practice, the basic patch panel we just looked at in figure 3-11 is practical for
low power levels. Another type of transmitter patch panel is shown in figure 3-13.

Figure 3-13. - Transmitting antenna patch panel.

This type of transmitting antenna patch panel is interlocked with the transmitter so
that no open jack connection can be energized and no energized patch cord can be removed.
This provides you with a greater degree of personnel and equipment safety.

Receive Multicoupler

Figure 3-14 is a filter assembly multicoupler that provides seven radio frequency
channels in the 14-kilohertz to 32-megahertz range. Any or all of these channels may be
used independently of any of the other channels, or they may operate simultaneously. You
can make connections to the receiver by means of coaxial patch cords, which are short
lengths of cable with plugs attached to each end.

Figure 3-14. - Electrical filter assembly.

A set of nine plug-in type filter assemblies is furnished with the equipment and covers
the entire vlf, lf, mf, and hf bands. Only seven of the assemblies may be installed at one
time, and you have the option of selecting those you need to cover the most used frequency
bands.

Figure 3-12 illustrates how the filter assembly is used in combination with other units
to pass an rf signal from an antenna to one or more receivers.

Transmit Multicouplers

Most multicouplers for the hf range are designed for use with either transmitters or
receivers, although some are used with both. There are a large number of channels in a
multicoupler so that many transmitters can be used at the same time on one antenna. This
is especially true in the 2- to 12-megahertz range.

Figure 3-15 shows you an antenna coupler group designed primarily for shipboard use.
Each coupler group permits several transmitters to operate simultaneously into a single,
associated, broadband antenna. You can see this reduces the total number of antennas
required in the limited space aboard ship.

Figure 3-15. - Antenna coupler group.

These antenna coupler groups provide a coupling path of prescribed efficiency between
each transmitter and its associated antenna. They also provide isolation between
transmitters, tunable bandpass filters, and matching networks.

TELETYPEWRITER AND FACSIMILE EQUIPMENT

In previous areas we have discussed different methods of voice communications. At
times, however, the message is too long for practical transmission by voice. To get
information or an idea across to another person far away, you may also need a chart, map,
or photograph. Teletypewriter (tty) and facsimile equipment allow us to do just that, with
ease. Let's see how this is done.

BASIC PRINCIPLES

To give you an idea of how intelligence is sent via teletypewriter, let's take a look
at the manual telegraph circuit. This circuit, shown in figure 3-16, includes a telegraph
key, a source of power (battery), a sounder, and a movable sounder armature. If the key is
closed, current flows through the circuit and the armature is attracted to the sounder by
magnetism. When the key is opened, the armature is retracted by a spring. With these two
electrical conditions of the circuit, intelligence can be transmitted by means of a
teletypewriter code. These two conditions of the circuit are referred to as MARKING and
SPACING. The marking condition occurs when the circuit is closed and a current flows; the
spacing condition occurs when it is open and no current flows.

Figure 3-16. - Manual telegraph circuit.

If the key at station A is replaced by a transmitting teletypewriter and the sounder
arrangement at station B is replaced by a receiving teletypewriter, the basic
teletypewriter circuit (loop) shown in figure 3-17 is formed.

Figure 3-17. - Simple teletypewriter circuit.

If a teletypewriter signal could be drawn on paper, it would resemble figure 3-18. This
is the code combination for the letter R. Shaded areas show intervals during which the
circuit is closed, and the blank areas show the intervals during which the circuit is
open. The signal has a total of seven units. Five of these are numbered and are called
INTELLIGENCE units. The first and last units of the signal are labeled START and STOP.
They are named after their functions: the first starts the signal, and the last stops it.
These are a part of every teletypewriter code signal: the START unit is always spacing,
and the STOP unit is always marking.

Figure 3-18. - Mark and space signals.

The teletypewriter signal is theoretically a perfect signal. The time between each unit
remains the same during transmission of the signal. The shift from mark to space (and vice
versa) is called a TRANSITION. A transition occurs at the beginning and end of each unit
when it shifts from mark to space or space to mark; a character may have two, four, or six
transitions.

When figuring the time duration of a signal character, no allowance for transition time
is made since the transition is instantaneous and is considered to have zero time
duration. The time duration for each unit is measured in milliseconds.

Q.10 What is the function of an antenna patch panel?
Q.11 What are the functions of a multicoupler?
Q.12 What are the terms used to describe an open or closed telegraph circuit?
Q.13 How many units are in a tty signal and what are they?